1. Field of the Invention
The present invention relates to an organic electroluminescent device and a display apparatus. In particular, the present invention relates to an organic electroluminescent device for emitting red light and a display apparatus using the same.
2. Description of the Related Art
In recent years, a display apparatus using an organic electroluminescent device (so-called “organic EL device”) is watched as a lightweight flat panel type display apparatus with high efficiency.
The organic electroluminescent device which configures such a display apparatus is provided on a transparent substrate composed of, for example, a glass and is prepared by stacking an anode composed of ITO (indium tin oxide: transparent electrode), an organic layer and a cathode in this order from the substrate side. The organic layer has a configuration in which a hole injection layer, a hole transport layer and an electron transporting light-emitting layer are stacked in this order from the anode side. In the thus configured organic electroluminescent device, an electron injected from the cathode and a hole injected from the anode are recombined in the light-emitting layer, and light which is generated during this recombination is extracted from the substrate side via the anode.
In addition to an organic electroluminescent device having the foregoing configuration, the organic electroluminescent device also includes a so-called top emission type which is configured by stacking a cathode, an organic layer and an anode in this order from a substrate side and in which by further configuring an electrode positioned in an upper portion (an upper electrode as the cathode or anode) by a transparent material, light is extracted from the upper electrode side on an opposite side to the substrate. In particular, in a display apparatus of an active matrix type which is prepared by providing a thin film transistor (TFT) on a substrate, a so-called top emission structure in which an organic electroluminescent device of a top emission type is provided on the substrate having TFT formed thereon is advantageous in view of enhancing an aperture ratio of a light-emitting portion.
Now, in the case of taking into consideration practical implementation of an organic EL display, not only an enhancement of light extraction by widening the aperture of an organic electroluminescent device but an enhancement of luminous efficiency of the organic electroluminescent device is necessary. Then, various materials and layer configurations for the purpose of improving the luminous efficiency have been investigated.
For example, so far as a red light-emitting device is concerned, there has been proposed a configuration in which a naphthacene derivative (including rubrene derivatives) is used as a dopant material with respect to a new red light-emitting material in place of a pyran derivative represented by DCJTB which has hither to been known (see, for example, JP-A-2000-26334 and JP-A-2003-55652 (especially paragraphs [0353] to [0357] and Table 11).
JP-A-2003-55652 also proposes a configuration for obtaining white emission by stacking a second light-emitting layer containing a penylene derivative and an anthracene derivative on a first light-emitting layer using a rubrene derivative as a dopant material.
Furthermore, there is proposed a configuration for obtaining white emission by doping a rubrene derivative on an electron transport layer or a hole transport layer which is disposed adjacent to a blue light-emitting layer (see JP-A-2004-134396).